Spinocerebellar ataxia (SCA) refers to a family of genetic diseases that cause progressive problems with gait and balance, as well as other debilitating symptoms. Even though the genes responsible for many of the SCA subtypes are known, and even though we know that they all are associated with damage of the cerebellum and other specific parts of the brain, there is no cure for SCA and we still lack an effective symptomatic treatment. We propose a novel approach using noninvasive transcranial magnetic stimulation (TMS) to improve balance, gait, and posture in patients with SCA. We will recruit 20 patients with genetically-confirmed SCA. Half will be randomly assigned to a real intervention, and half to a sham (i.e., control) intervention. The TMS intervention will consist of 20 stimulatio sessions over a four week period. At baseline and at follow-up, all patients will undergo comprehensive assessments including several SCA rating scales, along with sophisticated tests of balance (i.e., walking, standing and muscle coordination). Patients will also complete a series of neurophysiologic tests to evaluate the function of the cerebellum and its connections before and after the intervention. This will help us test the clinical utility of the intervention and als gain new knowledge about the basis for the disability in SCA. In pilot studies we have shown already that TMS is safe when applied to the cerebellum and that it can improve balance in patients. We now will conduct a more systematic, larger, carefully controlled proof- of-principle clinical trial We anticipate that patients receiving real rTMS will show better balance, fewer falls, and improved mobility while those undergoing sham stimulation will show no benefits. If our prediction is correct, this study will provide evidence-based support for a new treatment to improve the lives of patients with SCA, and the proposed quantitative evaluations will examine possible objective end-points for a future, larger multi-site clinical trial.